An ejector shown in Patent Document 1, for example, is known as a conventional ejector. In the ejector of Patent Document 1, a nozzle includes a throat portion most-reduced in passage cross-sectional area, and a divergent portion enlarged in passage cross-sectional area toward a downstream side from the throat portion. The divergent portion has a middle part on an upstream side, and an outlet part on a downstream side.
A divergent angle θ1 of a passage wall surface of the middle part is configured to be constant within the middle part. A divergent angle θ2 of a passage wall surface of the outlet part is configured to be larger than the divergent angle θ1.
When the fluid flowing into the throat portion in a gas-liquid two-phase state is depressurized, a gas content in the fluid increases in accordance with the depressurizing in the outlet part, especially. In the ejector of Patent Document 1, the divergent angle θ2 of the outlet part is made to be larger than the divergent angle θ1 of the middle part in accordance with the increase of the gas content. Thus, a pace of expansion in passage cross-sectional area is larger in the outlet part than in the middle part. Therefore, the fluid can be easily accelerated in the divergent portion, and a nozzle efficiency can be improved steadily.